1. Field of the Invention
The present invention relates to a device for generating optical energy within an optical fiber. Specifically, the invention uses a material within the fiber as the source of optical energy. Because the light source is within the fiber, the invention has advantages over prior art where the light is generated from outside of the fiber and must be guided into the fiber.
2. Description of the Background Art
Optical fibers are widely used in communication, sensing, illumination, imaging, inspection and medical applications. These applications use a fiber optic strand to transmit light from a light emitting source at one end of the fiber to a destination at the other end of the fiber. In conventional fiber optic devices the light source has been outside of the fiber. This requires lenses, reflectors or a combination of these or other means to channel the light into the relatively small aperture or "end" of the fiber.
These methods suffer from poor coupling efficiency because the optical emission from the light source has a wide angle of dispersion and the fiber aperture is a narrow angle. An incandescent source has typically been used which has a filament, or light emitting body, which is physically much larger than the fiber aperture. As a result, the focusing by the optical elements down to an area comparable to the fiber core is inefficient.
In U.S. Pat. Nos. 4,573,761; 4,730,895 and 4,860,172 light is generated at a location external to the fiber via conventional means and is introduced into the fiber end. U.S. Pat. No. 4,573,761 discloses a fiber optic probe made up of a bundle of fibers. One of the fibers in the bundle is used to transmit laser light to a target to be probed. A portion of the light reflected from the target enters the ends of the other fibers in the bundle and is detected. U.S. Pat. No. 4,730,895 uses an incandescent source and lens to introduce light into the end of a bundle of optical fibers U.S. Pat. No. 4,860,172 uses a reflector and lens to focus light into the fiber end.
U.S. Pat. Nos. 3,578,972 and 3,578,973 use a phosphorescent material as the light source. However, the material is external to the fiber and the emitted light is still introduced into the fiber end. U.S. Pat. No. 4,661,711 uses a fluorescent material within the fiber but only as a reference standard. The fluorescent material is excited by light entering the fiber through the fiber end. The excited fluorescent material then produces a constant reference light at the other end of the fiber which is independent of the source light.
The article "Electric-Discharge Sensor Utilizing Fluorescent Optical Fiber," published in July of 1989, uses a fluorescent material inside the fiber but only as a sensor of an electric discharge. Thus, while the article describes an invention which uses a luminescent optical fiber to receive energy outside of the aperture of the fiber's end, it is being used only as a detector to sense an unfixed, random radiation event.